Research On Deformation And Stability Of The Combined Retaining Structure Of Diaphragm Wall And Multi-row Steel Sheet Piles In Soft Soil Area

The deep foundation pit is getting closer and closer to the surrounding buildings,the construction space is getting smaller and smaller,and the overload near the foundation pit is getting larger and larger.In view of the features of the deep foundation pit in soft soil area,the combined retaining structure consisted of diaphragm wall and multi-row steel sheet piles is proposed.Firstly,the new retaining structure’s deformation and stability characteristics are analyzed.Then,the application effect and economic benefit of the engineering examples are analyzed and compared.Finally,numerical simulation overall analyzes the influence law of the main design parameters of the combined retaining structure,and some design optimization suggestions are proposed,which can be used as reference for engineering application.The paper’s research conclusions are as follows:(1)The working mechanism of the combined retaining structure can be divided into two aspects:for one thing,it has anchorage and synergy in the horizontal direction,and it can be regarded as the anchorage retaining structure and the frame retaining structure at different excavation stages.For another,it acts to transfer load and reinforce the foundation in the vertical direction,which is beneficial to control the deformation and stability of the foundation pit.(2)The stability analysis of the combined retaining structure shows that the presence of multi-row steel sheet piles increases the stability factor of the foundation pit to some degrees,delays the development of the plastic zone,and benefits the stability.(3)Analysis of engineering examples shows that the north maximum horizontal displacement of the diaphragm wall reduces about 7%-24%compared with diaphragm wall on the south side,which uses the combined retaining structure,and the north maximum ground settlement behind the pit reduces about 12%-57%.Moreover,the combined retaining structure is conducive to construction,shortens the construction period,reduce project cost,and has high sustainable economic benefits,which shows that it has good application effect and obvious economic benefits.(4)The paper obtains HSS model stiffness’value range、multiple relationship and recommended value in Ningbo area by the back analysis.On this basis,a way to quickly obtain the main parameters of HSS model based on the survey data is proposed.(5)By comparing the results of field measurement and numerical simulation,the rationality of numerical simulation analysis is verified,and the impact of the main design parameters on the combined retaining structure’s deformation is further analyzed.The corresponding laws of change and engineering suggestions are as follows:1)With the increase of the row spacing of the combined retaining structure,the horizontal displacement of diaphragm wall first decreases,then increases and then decreases,the ground settlement groove becomes widener,and the law of bulge at the bottom of the pit is the same as the horizontal displacement of diaphragm wall.Generally speaking,when the row spacing is 4m,the deformation control is better.Htan(45°-φ′/2) can be used to control the width of the combined retaining structure.If they are arranged at equal intervals,the average value should be taken.2)With the increase of the length of the steel sheet pile,the deformation of the foundation pit continues to decrease,the pile length is closely related to the excavation depth of the foundation pit,so the pile length should refer to the foundation pit depth.3)The deformation of the combined retaining structure is basically not affected by the change in the thickness of the top connecting plate.The thickness of the top connecting plate can be determined according to conventional construction.4)The foundation pit’s deformation is smaller when the combined retaining structure is rigidly connected.Therefore,it is recommended to use rigid connection.5)Under equal overload,with the rows of steel sheet piles increasing,the ground settlement around the foundation pit decreases.When the rows of steel sheet piles is fixed,the maximum ground settlement increases with the increase of overload after the pit.When the pit edge overload is equal to 0-20kPa,one row of steel sheet piles should be taken;when the pit edge overload is equal to 30-40kPa,two rows of steel sheet piles should be taken.It is recommended that the rows of steel sheet piles used in the combined retaining structure should be determined according to the overload strength.